1. Field of the Invention
The present invention relates to a photoconductor for electrophotography, and more particularly to a photoconductor for electrophotography with a high sensitivity and excellent characteristics in repeated use.
2. Description of the Prior Art
Photosensitive materials which have heretofore been used in photoconductors for electrophotography include inorganic photoconductive substances such as selenim and selenium alloys, dispersions of inorganic photoconductive substances such as zinc oxide and cadmium sulfide in resin binders, organic polymeric photoconductive substances such as poly-N-vinylcarbazole and polyvinylanthracene, organic photoconductive substances such as phthalocyanine compounds and bisazo compounds, and dispersions of such organic polymeric photoconductive substances in resin binders, and vacuum evaporated film of such organic polymeric photoconductive substances.
Photoconductors are required to have a function of maintaining a surface electric charge in the dark, a function of generating an electric charge upon receiving light, and a function of transporting an electric charge upon receiving light. They are classified into two types of photoconductors, namely so-called monolayer type photoconductors, and so-called laminate type photoconductors. The former comprises a single layer having all of the above-mentioned three functions, and the latter comprises functionally distinguishable laminated layers, one of which contributes mainly to the generation of electric charge, and another of which contributes to the retention of surface electric charge in the dark and the transportation of electric charge upon receiving light.
In an electrophotographic method using a photoconductor of the kind as mentioned above, for example, the Carlson's system is applied to image formation. The image formation according to this system comprises steps of subjecting a photoconductor in the dark to corona discharge to charge the photoconductor, illuminating the surface of the charged photoconductor with imagewise light based on a manuscript or copy bearing, e.g., letters and/or pictures to form a latent electrostatic image, developing the formed latent electrostatic image with a toner, and transferring the developed toner image to a support such as a paper sheet to fix the toner image on the support. After the toner image transfer, the photoconductor is subjected to the steps of removal of the electric charge, removal of the remaining toner (cleaning), neutralization of the residual charge with light erasure, and so on to be ready for reuse.
Photoconductors for electrophotography in which use is made of a photosensitive organic compound have recently been put into practical use by virtue of the advantageous features such as flexibility, thermal stability and/or a film forming capacity. A variety of charge transporting substances are known, for example, an oxadiazole compound is disclosed in U.S. Pat. No. 3,189,447, a pyrazoline compound is disclosed in Japanese Patent Application Publication No. 2,023/1984, a hydrazone compound is disclosed in Japanese Patent Application Publication No. 42,380/1979 and Japanese Patent Application Laying-open No. 101,844/1982, a triallylamine is disclosed in Japanese Patent Application Laying-Open No. 32,327/1983 and a stilbene compound is disclosed in Japanese Patent Application Laying-open No. 198,043/1983.
Although organic materials have a number of advantageous features mentioned above with which inorganic materials are not endowed, however, the fact is that there have been obtained no organic materials fully satisfying all the characteristics required of a material to be used in photoconductors for electrophotography at the present. Particular problems involved in organic materials have been concerned with photosensitivity and characteristics in continuous repeated use.